Wednesday 4 January 2012 04.01 EST
First published on Wednesday 4 January 2012 04.01 EST

The man on the Clapham omnibus is a staple of London folklore, a century-old personification of reasonable suburban opinion and average metropolitan means. He is a fellow who – in my mind at least – keeps his door knocker polished and owns a sensible sort of mac. He will live on for many more decades. But this year his importance could be eclipsed by a different touchstone citizen: the voter on the number 48.

Bus policy is already a bruising battleground in the London mayoral election campaign. Frontrunners Boris Johnson, the Conservative incumbent, and his Labour challenger and predecessor, Ken Livingstone, are making very different overtures. Johnson is pointing proudly to his removal of articulated "bendy" buses from the dozen of London's 700 routes they operated on, and to his forthcoming introduction of a new model double-decker, though only eight have so far been ordered to grace a total London fleet of 8,500.

Livingstone is casting a wider net. His Fare Deal campaign pledges to "wipe out" the latest of Johnson's four consecutive inflation-plus price rises across the entire public transport network of buses, trains and trams, and to do so from October. He makes a particular point of promising to bring down bus fares.

The Labour candidate's chance of completing a remarkable political comeback depends heavily on his enthusing the sorts of Londoners who travel on routes such as the 48. It connects the public transport hubs of Walthamstow Central and London Bridge, conveying many workers to and from the employment magnet of the City. Riding on it, especially in the morning rush hour – as I often do when travelling from my home to City Hall and as I did on Tuesday when London went back to work – provides telling insights into the capital's economic metabolism and glimpses of the lives of those of its citizens feeling the worst effects of the financial squeeze.

Inhabitants of Walthamstow itself have three public transport options for reaching places of work in the Square Mile: the overground train to Liverpool Street; the underground southbound, changing lines en route; or the number 48 all the way. The latter is the cheapest, and it shows. Passengers typically range from north-east London equivalents of that legendary Clapham traveller to others who, I'd guess, lead less certain lives. Dress codes range from budget white-collar (primarily the women) to building site durable (mostly men). Once past the handbag wholesalers, council blocks and occasional Georgian terraces of Hackney Road, they disembark in numbers along Bishopsgate and melt into the City's ancient side-street labyrinth.

Route 48 brings to life the statistics showing that the bus is the public transport mode used most heavily by Londoners on low pay – people who will most notice the five pence increase per journey with which Johnson has welcomed them to the new year. Their numbers often swell when economic times are hard because the alternatives cost more. Livingstone and his Fare Deal activists have been urgently reminding anyone who will listen that before the Tory mayor came to power in 2008, a single bus fare was just 90p – compared with £1.35 now.

There are signs that the Fare Deal campaign is drawing blood. Johnson's media chums are querying Livingstone's maths and honesty, while the official Johnson campaign argues that Fare Deal demonstrates financial irresponsibility. Yet when the latest increases came into effect Johnson himself was not to be seen, with his lieutenants declining to say if he was still on holiday abroad or just pretending to be.

Meanwhile, House of Commons library figures have shown that London has the most expensive public transport of any major city in the world. Johnson's latest rises have pushed that up by 5.6% across the board. Livingstone is calling them "a stealth tax" symbolic of wider Tory attitudes. Will enough voters on the number 48 take note? If they do, both they and their famous Clapham counterpart could be paying less before the end of this year.